1. Field of the Invention:
The present invention relates to a waste treatment system in a polishing apparatus, and more particularly to a waste treatment system in which waste gas and waste liquid discharged from a polishing apparatus can be treated.
2. Description of the Related Art:
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused on by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, such a polishing apparatus has not been installed in a clean room because dust particles and harmful gas are generated by the polishing operation of the polishing apparatus. Therefore, semiconductor wafers are transported into the clean room by means of a wafer carrier after they are polished by the polishing apparatus installed outside the clean room, and then the semiconductor wafers are processed to form device layers by processing apparatuses installed in the clean room.
However, as described above, high integration in a semiconductor device demands the semiconductor wafer to be multilayer, it is therefore necessary to make each surface of the multilayer flat for photolithography. In order to increase the productivity of the semiconductor device, the polishing apparatus is required to be installed in the clean room of a semiconductor manufacturing plant.
In the polishing apparatus, abrasive liquid is supplied from a nozzle onto an abrasive cloth attached to an upper surface of a turntable. The abrasive liquid contains abrasive material such as silicon dioxide (SiO.sub.2) or cerium dioxide (CeO.sub.2) having a diameter of 1 .mu.m or less in a liquid.
Further, in order to perform chemical polishing in addition to mechanical polishing, acid or alkali may be added to the abrasive liquid. In this case, acid waste gas or alkaline waste gas are liable to be discharged from the polishing apparatus.
However, since a conventional polishing apparatus is not provided with a waste gas treatment apparatus, acid waste gas or alkaline waste gas discharged from the polishing apparatus pollutes air in the clean room and is a serious cause of lowering the yield of the semiconductor devices.
Further, waste liquid discharged from the polishing apparatus contains abrasive material and particles generated by the polishing operation. Because discharge of such waste liquid containing abrasive material and particles generated by the polishing operation causes environmental pollution, it is therefore necessary to make the waste liquid clean and to discharge clean liquid from the polishing apparatus.